1. Field of the Invention
This invention relates to a process of producing multicolor optical filters and, more particularly, to a process of producing multicolor optical filters used for color image pick-up tubes, color solid state image pick-up devices, etc.
2. Description of the Prior Art
For color image pick-up tubes or color solid state image pick-up devices such as charged coupled devices (C.C.D.) and charged injection devices (C.I.D.), multicolor stripe or mosaic form optical filters are used. A multicolor optical filter is usually composed of three colors of red, green, and blue or three colors of cyan, magenta and yellow regularly arranged in a stripe or mosaic form. At the same time the color composition of such multicolor optical filters is not always limited to three color systems and multicolor optical filters composed of two colors or four or more colors are sometimes used.
Conventional multicolor optical filters include filters prepared using dichroic mirrors as described in, for example, Japanese Patent Publication No. 8590/65 and Japanese Patent Application (OPI) No. 3440/77 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application") and the filters prepared by dyeing polymer layers with dyes as described in Japanese Patent Application (OPI) Nos. 37237/72, 63739/73 and 66853/73 and Japanese Patent Publication No. 248/78 but these processes are all complicated and troublesome since a pattern must be formed for each color in the system. For example, the steps of coating a photoresist, image-wise exposure of the photoresist (which in turn involves precise alignment of a mask on the photoresist layer), development of the exposed layer, coloring/decoloring, and removing the resist, must be carried out for each color in the filter.
In practice, additional steps may be necessary to obtain excellent multicolor optical filters. For example, in the case of producing multicolor optical filters by repeating several times the steps of coating a photoresist such as gelatin dichromate, image-wise exposure, formation of relief patterns by development, and coloring; a counterplan is required to prevent the occurrence of color mixing caused when colored patterns formed in a previous coloring step mix with a different color in a subsequent coloring step. For this purpose, it may be necessary to form a protective layer which is not dyed on the surface of a pattern bearing layer in between the coloring steps as described in Japanese Patent Application (OPI) No. 37237/72, which complicates the production process and makes the cost for multicolor optical filters very high.
To overcome these difficulties, attempts using silver salt color photographic materials (herein they are simply referred to as color films) have been made. In such a process the desired multicolor optical filter is prepared by exposing a color film of a type in which the couplers are contained in the color film or of a type in which the couplers are incorporated in the developers, through red, green and blue master filters or cyan, magenta, and yellow master filters, forming a color filter composed of cyan, magenta, and yellow colors or red, green, and blue colors by an ordinary color development, sticking the color filter on a glass disc such as a face plate of an image pick-up tube or camera tube, and further applying thereon a thin glass plate. In the color film used in the above-described process, the size of silver halide grains in the silver halide emulsion layers is considerably large and also the silver halide emulsion layers are in a multilayer structure, each having a sensitivity in each spectral wavelength region. Consequently, scattering of light in the silver halide emulsion layers is severe and hence the resolving power of the color film is not so high.
Also, Japanese Patent Application No. 78313/78 discloses a technique of obtaining a very high resolving power using a combination of a photographic material having conventional black-and-white fine grain silver halide emulsions and color development of the type in which the couplers are incorporated in the developers. However, this technique requires at least three light exposure and color development steps and hence is very complicated.
Furthermore, in conventional processes it is necessary to use a specific mask in which red, green, and blue filters are arranged in a mosaic form for exposure and complicated steps are required to make the mask precise.